Print out copies of Goatse on photo paper, hide them in your drawers and cabinets, and ask a nearby coworker to make a note of the day and time if they hear anyone scream "Oh God, what the fuck is that?" If someone goes in there and doesn't scream, keep n eye out for them giving you disgusted looks.
Or install
this, leave the computer on when you're gone, and check for incriminating pictures when you get back.